Time-lag fuse with ribbon fuse link folded in longitudinal
and in transverse direction



Dec. 13, 1966 F J, KOZACKA 3,291,943

TIME-LAG FUSE WIJTH RIBB'ON FUSE LINK FOLDED IN LONGITUDINAL AND IN TRANSVERSE DIRECTION Filed Jan. 7, 1966 2 Sheets-Sheet 1 INVENTOR FREDERICK J. KOZACKA BY ATTY.

Dec. 13, 1966 F .1. KOZACKA TIME-LAG FUSE WITH RIBBON FUSE LINK FOLDED IN LONGITUDINAL AND IN TRANSVERSE DIRECTION Filed Jan. 2 Sheets-Sheet 2 FIG. 5

FIG. 7

INVENTOR FREDERICK J. KOZACKA BY Wm WM United States Patent Ofirice 3,291,943 TIME-LAG FUSE WITH RIBBON FUSE LINK FOLDED IN LONGITUDINAL AND IN TRANSVERSE DIRECTION Frederick J. Kozacka, South Hampton, N.H., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Jan. 7, 1966, Ser. No. 519,276 6 Claims. (Cl. 200-120) This is a continuation-in-part of my co-pending patent applications Ser. No. 414,630 and Ser. No. 414,750, both filed on Nov. 30, 1964.

The invention relates to time-lag fuses, and more particularly to time-lag fuses for motor circuits.

The structures disclosed and claimed in my above referred-to patent applications are adapted for relatively high current ratings.

It is one object of the present invention to provide time-lag fuses having substantially the same performance characteristics as the time-lag fuses disclosed and claimed in my above-referred-to patent applications, but being particularly adapted for relatively small current ratings, or current ratings less than 100 amps.

It is another object of this invention to provide timelag fuses having a single fuse link whose current-carrying capacity is relatively limited and whose fuse link is well centered in regard to the casing of the fuse, i.e. has a sufficiently even spacing from the casing of the fuse.

Another object of this invention is to provide timelag fuses for relatively small current ratings having a blowing time of about ten, or more than ten, seconds at overload currents in the order of five times the rated current of the fuse, and operating as current-limiting fuses on occurrence of currents of short-circuit current proportions.

Still another object of this invention is to provide timelag fuses of the kind disclosed in my above referred-topatent applications, or of a similar kind, including means for reducing the heat flow in a direction longitudinally of the fuse structures, thus tending to reduce the minimum fusing current and to increase time-lag in terms of blowing time at given multiples of the rated current of the fuse structures.

These and other objects of the invention and advantages thereof will become more apparent from the accompanying drawings and the following description of preferred embodiments of the invention.

In the drawings:

FIG. 1 is a top-plan view of an electric fuse being a first embodiment of this invention;

FIG. 2 is substantially a vertical section of the structure of FIG. 1;

FIG. 3 is a section along 3-3 of FIG. 1;

FIG. 4 is an isometric view of the fuse link structure forming part of the fuse shown in FIGS. 1-3;

FIG. 5 is substantially a vertical section of another electric fuse being a second embodiment of this invention;

FIG. 6 is a section along 6-6 of FIG. 5; and

FIG. 7 is an isometric view of a fuse link structure similar to that shown in FIGS. 5 and 6, but including a modification tending to reduce axial heat flow and to increase time-lag.

Referring now to the drawings, and more particularly to FIGS. 1 to 4 thereof, numeral 1 has been applied to indicate a tubular casing of insulating material. Casing 1 is closed on both ends thereof by terminal elements in the form of caps 2 mounted on the axially outer ends of casing 1. Blade contacts 3 project transversely across terminal caps 2 and hollow pins 4 project transversely through casing 1 and blade contacts 3. Pins 4 are preferably of the type disclosed and claimed in US. Patent 2,939,935, issued June 7, 1960, and US. Patent 3,007,020,

3,291,943 Patented Dec. 13, 1966 issued October 31, 1961. Reference numeral 5 has been applied to indicate pins which are driven into the ends of hollow pins 4 to expand the latter. Casing 1 is filled with a pulverulent arc-quenching filler 6, preferably quartz sand. The blade contacts 3 and the caps 2 on opposite ends of casing 1 are conductively interconnected by a ribbon fuse link of a high fusing point metal such as silver or copper. Reference numeral 7 has been applied to generally indicate this fuse link. Washers 8 of asbestos fibers or of a similar material are interposed between the axially outer ends of casing 1 and caps 2. Fuse link 7 includes an axially inner portion 7a and axially outer connector portions 7b. The axially inner portion is wedge-shaped and formed by a pair of flanges 7 and 7 enclosing an acute angle at. The axially inner portion 7a of fuse link 7 has a predetermined maximum cross-sectional area and defines serially related points of reduced cross-sectional area. Each of the three serially related points of reduced cross-sectional area is formed by a transverse line of circular perforations clearly shown in FIG. 4. Flanges 7' and 7" of the axially inner portion 7a of fuse link 7 support an overlay 9 of a link-severing low fusing point metal. Overlay 9 is preferably arranged in the way disclosed and claimed in my US. Patent 2,988,620, issued June 13, 1961. Overlay 9 may be of tin, or an alloy of tin, or of indium or cadmium, depending upon the temperature at which it is desired to sever the fuse link in case of relatively small protracted overloads. As mentioned above fuse link 7 further includes the axially outer integral connector tabs 7b each having a smaller cross-sectional area than the aforementioned maximum cross-sectional area of the axially inner wedge-shaped link portion 7a, but a larger cross-sectional area than any of the points of reduced cross-sectional area of the axially inner link portion 7a. This geometry is necessary in order to compel under short-circuit conditions initial fusion to occur at the points of reduced cross-sectional area of the axially inner portion 7a of fuse link 7 rather than at any point of the axially outer connector tab portions 7b. Each connector tab portion 7b is bent twice at spaced points in a direction longitudinally of fuse link 7. As a result of these two bends connector tab portions 711 form a first loop 7b toward the center of the axially inner portion 7a and form a second loop 7b" away from the center of the axially inner portion and toward one of the blade contacts 3 and terminal caps 2. Loops 7b and 7b greatly limit the dissipation of heat generated in the axially inner portion 7a of fuse link 7, and thus tend to limit the current-carrying capacity of the fuse structure, i.e. they require the mass of the fuse link 7 to be relatively large to obtain a predetermined minimum fusing current, and this, in turn, results in relatively long time lags, particularly in the range of five times the rated current of the fuse. The flange 7' of axially inner portion 7a is arranged in the plane defined by blade contacts 3, as is clearly apparent from FIG. 2, and thus the hottest portion of the fuse link 7 is positioned close to the longitudinal axis of the fuse tube or casing 1, and relatively evenly spaced from the latter. The axially outer end of each connector tab 7b, i.e. the loop 7b" thereof, encloses an obtuse angle with one of blade contacts 3. As a result of this particular geometry of loop portions 7b, 7b" the axially inner portion 7a of fuse link 7 can be arranged close to the longitudinal axis of casing 1, as mentioned above.

On occurrence of relatively small protracted overloads the axially inner portion 7a of fuse link 7 is severed in the center thereof by a metal diffusion process involving the low fusing point metal overlay 9. Final circuit interruption is achieved upon a predetermined burn-back in opposite direction from the point where the fuse link 7 has been severed initially. On occurrence of major fault currents three series breaks are formed each at .a point of reduced cross-sectional area of the axially inner portion 7a of fuse link 7 In FIGS. to 7 the same reference characters as in FIGS. 1 to 4 have been applied to indicate like parts. Casing 1 is closed by terminal caps 2 which are not provided with blade contacts and houses a fuse link 7 of silver or copper conductively interconnecting caps 2 and submersed in a pulverulent arc-quenching filler 6. The

axially inner portion 7a of fuse link 7 includes two flanges 7 and 7" which enclose the acute angle 04. The axially inner portion 7a of fuse link 7 has a predetermined maximum cross-sectional area and defines three serially related points of reduced cross-sectional area which determine the fusing i -t of the fuse link structure. These points of reduced cross-sectional area are formed by transverse lines of circular perforations. Flanges 7 and 7" support a link-severing overlay 9 of a soft low fusing point metal such as, for instance, tin, or an appropriate alloy thereof. Fuse link 7 further includes the connector tab portions 7b. Each connector tab portion 7b is bent twice in a direction longitudinally of fuse link 7 and includes an axially inner loop portion 7b and an axially outer loop portion 7b. The axially inner loop portion 7b and the axially outer loop portion 712" shown to the left of FIGS. 5 and 7 are formed by an extension of flange 7 of axially inner portion 7a and the axially inner loop portion 7b and the axially outer loop portion 7b" shown to the right of FIGS. 5 and 7 are formed by an extension of flange 7 of the axially inner portion 7a. This results in a positioning of the axially inner portion 7a close to the longitudinal axis of fuse tube or casing 1, thus tending to minimize heat losses from the axially inner portion 7a of fuse link 7. The zig-zag or loop geometry of connector tabs 7b tends likewise to minimize heat exchange between the axially inner portion 7a of fuse link 7 and its surroundings, particularly terminal caps 2.

In the modification of the fuse link structure of FIGS. 5 and 6 illustrated in FIG. 7 the connector tabs 7b have a cross-sectional area progressively decreasing toward one of the terminal elements, i.e. toward one of caps 2. Each connector tab 7b tapers axially outwardly and has a minimum cross-sectional area at the axially outer end thereof, i.e. the end thereof adjacent one of terminal caps 2. The cross-sectional area of this point of minimum crosssectional area of each connector tab 7b exceeds the crosssectional area of any point of reduced cross-sectional area of flange portions 7' and 7". This is necessary to preclude arc-initiation under short-circuit current conditions at a point of connector tabs 7b rather than at the points of reduced cross-sectional area of flange portions 7 and 7". The taper of connector tabs 7b while greatly reducing heat exchange in a direction longitudinally of the fuse structure still makes it possible to maintain the hottest region of fuse link 7 immediately adjacent the center thereof, thus insuring at small overloads formation of the initial break adjacent the center of the fuse link 7, i.e. where overlay 9 is located. The closer any point of terminal tabs 7b to caps 2, the smaller the thermal impedance required to achieve just the right heat flow in a direction longitudinally of the fuse structure and the taper geometry of connector tabs 7b is an outgrowth of this fact.

It will be apparent from the foregoing that the flanges 7 and 7 form juxtaposed areas of the fuse link 7 which establish parallel current paths and that flanges 7' and 7" define an edge at the intersection of the planes thereof which extends in a direction substantially longitudinally of casing 1. Flanges 7 and 7" are portions of the fuse link 7 mutually heating each other.

It will be understood that I have illustrated and described herein several preferred embodiments of my invention, and that various alterations may be made therein without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. A time-lag fuse comprising:

(a) a casing of insulating material;

(b) a pulverulent arc-quenching filler inside said casing;

(c) a pair of terminal elements closing the ends of said casing; and

(d) a ribbon fuse link of a high fusing point metal inside said casing surrounded by said arc-quenching filler and conductively interconnecting said pair of terminal elements, said fuse link including an axially inner wedge-shaped portion formed only by a pair of flanges enclosing an acute angle, said pair of flanges defining serially related points of reduced crosssectional area and said pair of flanges supporting an overlay of a link-severing low-fusing point metal, said fuse link further including a pair of axially outer internal connector tabs each formed by an extension of one of said pair of flanges and each having a larger cross-sectional area than any of said points of reduced cross-sectional area of said pair of flanges and each of said pair of connector tabs being bent in a direction longitudinally of said fuse link at a first point to form a first loop toward the center of said pair of flanges and each of said pair of connector tabs being bent in a direction longitudinally of said fuse link at a second point spaced from said first point to form a second loop away from the center of said pair of flanges and toward one of said pair of terminal elements.

2. A time-lag fuse as specified in claim 1 comprising a pair of terminal caps and a pair of blade contacts each projecting transversely through one of said pair of terminal caps wherein one of said pair of flanges is arranged in a plane defined by said pair of blade contacts and wherein the axially outer end of each of said pair of connector tabs encloses an obtuse angle with one of said pair of blade contacts.

3. A time-lag fuse as specified in claim 1 wherein one of said pair of connector tabs forms an axial extension of one of said pair of flanges of said axially inner fuse link portion and wherein the other of said pair of connector tabs forms an axial extension of the other of said pair of flanges of said axially inner fuse link portion.

4. A time-lag fuse as specified in claim 1 wherein each of said pair of connector tabs has a cross-sectional area progressively decreasing from said pair of flanges toward said pair of terminal elements, each of said pair of connector tabs having a minimum cross-sectional area at the end thereof adjacent one of said pair of terminal elements, and said minimum cross-sectional area being larger than said points of reduced cross-sectional area of said pair of flanges.

5. A time-lag fuse com rising:

(a) a casing of insulating material;

(b) a pulverulent arc-quenching filler inside said casing;

(c) a pair of terminal elements closing the ends of said casing; and

(d) ribbon fuse link means of a high fusing point metal inside said casing surrounded by said arc-quenching filler and conductively interconnecting said pair of terminal elements, said fuse link means having axially inner juxtaposed areas forming parallel current paths, said axially inner areas defining serially related points of reduced cross-sectional area and supporting an overlay of a link severing low-fusing point metal, said fuse link means further including axially outer integralconnector tabs having a cross-sectional area progressively decreasing from said axially inner areas toward said pair of terminal elements and having a minimum cross-sectional area at the ends thereof adjacent said pair of terminal. elements larger than said points of reduced cross-sectional area of said axially inner areas, and said connector tabs being bent in a direction longitudinally of said fuse link means at a first point to form first loops toward the center of said axially inner areas and said connector tabs being bent in a direction longitudinally of said fuse link means at a second point to form a second loop away from the center of said axially inner areas and toward said pair of terminal elements.

6. A time-lag fuse comprising:

(a) a casing of insulating material;

(b) a pulverulent arc-quenching filler inside said casing;

(c) a pair of terminal elements closing the ends of said casing; and

(d) a ribbon fuse link of a high fusing point metal inside said casing surrounded by said arc-quenching filler and conductively interconnecting said pair of terminal elements, said fuse link including an axially inner portion bent transversely to form an edge extending in a direction substantially longitudinally of said casing, said axially inner portion of said fuse link defining serially related points of reduced crosssectional area and supporting an overlay of a link severing low fusing point metal, said fuse link further including a pair of axially outer integral connector tabs each having a cross-sectional area progressively decreasing from said axially inner portion toward one of said pair of terminal elements and each of said pair of connector tabs having a minimum crosssectional area at the end thereof adjacent one of said pair of terminal elements larger than any of said points of reduced cross-sectional area of said axially inner portion of said fuse link, and each of said pair of connector tabs being bent in a direction longitudinally of said fuse link at a first point to form a first loop toward the center of said axially inner portion of said fuse link and each of said pair of connector tabs being bent in a direction longitudinally of said fuse link at a second point spaced from said first point to form a second loop toward one of said pair of terminal elements.

References Cited by the Examiner UNITED STATES PATENTS 2,157,906 5/1939 Lohausen 200-131 3,029,328 4/1962 Kozacka 200-13 1 3,189,712 6/1965 Kozacka 200-131 FOREIGN PATENTS 133,049 4/ 1933 Austria.

450,458 5/ 1926 Germany.

673,990 4/ 1939 Germany.

372,528 5/ 1932 Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

25 H. B. GILSON, Assistant Examiner. 

1. A TIME-LAG FUSE COMPRISING: (A) A CASING OF INSULATING MATERIAL; (B) A PULVERULENT ARC-QUENCHING FILLER INSIDE SAID CASING; (C) A PAIR OF TERMINAL ELEMENTS CLOSING THE ENDS OF SAID CASING; AND (D) A RIBBON FUSE LINK OF A HIGH FUSING POINT METAL INSIDE SAID CASING SURROUNDED BY SAID ARC-QUENCHING FILLER AND CONDUCTIVELY INTERCONNECTING SAID PAIR OF TERMINAL ELEMENTS, SAID FUSE LINK INCLUDING AN AXIALLY INNER WEDGE-SHAPED PORTION FORMED ONLY BY A PAIR OF FLANGES ENCLOSING AN ACUTE ANGLE, SAID PAIR OF FLANGES DEFINING SERIALLY RELATED POINTS OF REDUCED CROSSSECTIONAL AREA AND SAID PAIR OF FLANGES SUPPORTING AN OVERLAY OF A LINK-SEVERING LOW-FUSING POINT METAL, SAID FUSE LINK FURTHER INCLUDING A PAIR OF AXIALLY OUTER INTERNAL CONNECTOR TABS EACH FORMED BY AN EXTENSION OF ONE OF SAID PAIR OF FLANGES AND EACH HAVING A LARGER CROSS-SECTIONAL AREA THAN ANY OF SAID POINTS OF REDUCED CROSS-SECTIONAL AREA OF SAID PAIR OF FLANGES AND EACH OF SAID PAIR OF CONNECTOR TABS BEING BENT IN A DIRECTION LONGITUDINALLY OF SAID FUSE LINK AT A FIRST POINT TO FORM A FIRST LOOP TOWARD THE CENTER OF SAID PAIR OF FLANGES AND EACH OF SAID PAIR OF CONNECTOR TABS BEING BENT IN A DIRECTION LONGITUDINALLY OF SAID FUSE LINK AT A SECOND POINT SPACED FROM SAID FIRST POINT TO FORM A SECOND LOOP AWAY FROM THE CENTER OF SAID PAIR OF FLANGES AND TOWARD ONE OF SAID PAIR OF TERMINAL ELEMENTS. 